(a) Field of the Invention
The field of the invention relates to thrust reverser assemblies for jet aircraft engines, and more particularly, to a one-piece composite torque box for transmitting loads on the thrust reverser assembly to the engine and engine support structure.
(b) Background Art
Typical commercial aircraft gas turbine engines are surrounded and encapsulated by aerodynamic structural surfaces which form a nacelle. A typical nacelle structure 10 is shown in FIG. 1A, and this includes a forward fan cowl 12, and a thrust reverser cowl 14. This reverser cowl is part of the thrust reverser assembly which is included in most nacelles today.
An exemplary thrust reverser assembly 20 is shown in FIG. 1B. The thrust reverser forms a fan duct 22 during normal engine forward thrust operation. The assembly includes moving internal blocker doors and an outer sliding sleeve which, when actuated, block the fan flow and redirect it through grate-like, forward-guided vanes, or cascades 28 so as to produce reverse thrust. This reverse thrust is used for slowing the airplane upon landing. A typical thrust reverser 20, as shown in FIG. 1B, is made up of two cowl halves 30, 32. Each half hinges off the engine supporting strut, and engages a V-groove ring formed on the engine itself. FIG. 1B shows the semi-circular V-blade rings 34, 36 at the forward end of the reverser assembly which engage the V-groove in the engine. In this way, reverse thrust loads are transmitted to the engine and the strut.
The main structural part of the thrust reverser assembly which transmits the reverse thrust air loads on the cascade vanes out to the V-blade rings and the hinge and latch castings is called a torque box. First and second semi-circular torque boxes 40, 42 are shown installed in the first and second cowl halves 30, 32 in FIG. 1B. The reverse forces on the cascades "pull back" on the torque boxes, so as to subject parts of the box to tension loading; furthermore, the rod-like actuators which extend the two cowl halves also "pull back" on the torque boxes, these being connected to the torque boxes at a series of spaced apart bosses 44. Accordingly, it will be understood that the actuators and the cascades twist the box with respect to the fixed ends at the hinge and latch beams, so that the torque box is in torsion when the thrust reverser assembly is in operation.
FIG. 2A shows the two torque boxes 40, 42 installed in the cowl halves 30, 32, looking directly aft at the forward end of reverser assembly 20, and FIG. 2B shows an individual one of the torque boxes (40}removed from its associated cowl half to illustrate its overall configuration, most of the details of the torque box being omitted for purposes of clarity. As can be seen in FIG. 2B, the semi-circular torque box 40 is generally triangular in cross-section, and so has a generally planar inner or lower wall 46, bounded by an after edge 48 and a forward edge 50. The cascades are attached to the after edge 48 of the torque box, and the V-blade ring is attached to the forward edge 50. Wall 46 is thus subjected to tension during operation, and the actuators press rearward at bosses 44; the torque which is applied to the torque box is transmitted to its upper end 52, which is mounted to one of the castings 54, 56, which have hinge lugs by which the reverser is mounted on the strut. Similarly, at its lower end 58, the torque box is mounted to lower latch casting 60, 62. These hinge and latch castings (see FIG. 2A) are mounted to the engine strut so that the forces are transmitted thereto by the torque boxes.
FIG. 2C is a cross-section taken through the first cowl half 30 of FIG. 2A, showing the installation therein of a prior art-type torque box 40 configured generally as previously described, this cross-section being taken through one of the rib members of the torque box. As previously noted, the torque box is generally triangular in cross-section, and the grate-like cascades 28 (shown in phantom in FIG. 2C) are attached to the rearward edge 48 of wall 46, while the V-blade ring 34 is attached to the forward edge portion 50 of this wall, this V-blade ring being configured to engage the V-groove 64 on the engine casing 65 (also shown in phantom). The forward wall 66 of the torque box, in turn, extends to an outer corner where it is mated with the firewall 67 of the engine assembly. This firewall extends outwardly to an outer, flattened ring portion 68, a forward edge of which supports the fan cowling 12 of nacelle 10. A rearward portion of this flattened outer ring portion 68 supports the inner surface of the leading edge portion 69 of the outer sleeve 70 of the reverser cowl 14. It is this outer sleeve 70 which moves aftwards from the torque box structure when actuated by the actuator assemblies (not shown), thus allowing the air which is blocked from going rearward by the doors to be directed back through the cascades 28 in a forward direction, providing the desired braking action.
As can be seen from FIG. 2C, the prior art-type thrust reverser torque boxes are assembled from a large number of metallic details. The conventional torque box which is shown in this example is of a kind used in the General Electric/SNECMA CFM 56-3 engine installation for the Boeing 737-300, 400, and 500 series aircraft. Each of these torque boxes uses three stretch-formed aluminum extrusion corner members 72, 74, and 76, after and inner adhesively bonded doubled and tripled aluminum webs 78 and 80, a chem-milled titanium forward web 82, twelve inner forged aluminum ribs 84, and an aluminum built-up support structure 86, 86, for the aerodynamic bull-nose fairing which goes over the inner surface of the torque box. It will thus be appreciated that a great many manufacturing operations are required to produce the numerous metallic components from which each of the torque boxes is assembled, and that this is disadvantageous from an economic standpoint. Furthermore, in order to assemble these components together, a great many fasteners must be installed, and this is both costly and time consuming, and adds to the weight of the finished structure. Furthermore, because it is necessary to overlap the components in order to form joints in which the fasteners can be installed, the weight disadvantage is compounded.
Apart from the disadvantages in terms of cost and weight which have just been discussed, the built-up metallic torque box is a far from ideal structure for transmitting the forces which are applied to it. This is because, as is generally recognized, the most suitable structure for transmitting torque (and at the same time minimizing weight) is a tubular structure, while, for transmitting tension forces, a linear or planar structure is superior, and it is not efficient to construct a torque box 40 out of metallic details which combines these features to a satisfactory degree, yet which also meets the necessary weight limitations and is suitably configured to be mounted to the firewall, V-blade ring, and cascades in the manner previously described. The prior art torque box shown in FIG. 2C is at best a compromise in this regard, in that it is built up of the angular corner members and the spaced-apart aluminum ribs to achieve a compromise structure for transmitting these loads.
As will become apparent from a reading of the detailed description provided below, Applicant has solved the problems cited above by employing a torque box structure which is fabricated of graphite reinforced epoxy composite material. The generic advancement of composite materials to aircraft structures is, of course, known to those skilled in the art; a search of the patent literature has disclosed a number of patents related to such uses of composite materials, and these are listed as follows:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,710,412 Darrieux Dec. 01, 1987 4,471,609 Porter et al. Sep. 18, 1984 4,132,069 Adamson et al. Jan. 02, 1979 4,055,041 Adamson et al. Oct. 25, 1977 4,038,118 James Jul. 26, 1977 ______________________________________
Of these, Adamson et al. '041 and '069 both show an integral webbed structure, resembling a spoked wheel, which rigidly interconnects the outer nacelle and the engine so as to support the nacelle in its spatial relationship with the engine; Adamson et al. recite that it is preferable that this structure be fabricated from lightweight, high-strength composite materials, it being an object of the invention to reduce overall system weight.
Darrieux discloses a method of fabricating entire frames (e.g., for engines and aircraft) from resin-bonded filamentary material. The frame members are made by winding the filamentary material over a form (i.e., a mandrel) and then impregnating this material with hardenable resin, the hollow member which results being removable from the mold by providing a taper on the mandrel, or by the employment of stripping agents. The frame is then built up by securing these various members together.
Porter et al. show a lightweight, load-carrying engine core cowl which is made of a composite material, with air cooling being provided to the outer surface and interior of the cowl so as to preserve its load-carrying ability.
James shows a structure, such as an outer engine cowling, incorporating composite material reinforcing ribs made by wrapping a lightweight reinforcing material core with an adhesive tape containing continuous filament composite fibers. Metal inserts are positioned in the core to accept load-bearing fasteners, and loads transferred into the structure place the composite materials in tension or compression.
The review of the patent literature also disclosed a number of patents relating to engine mounting systems in general, and these are listed as follows:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,725,019 White Feb. 16, 1987 4,560,122 Parkinson et al. Dec. 24, 1985 3,288,404 Schmidt et al. Nov. 29, 1966 ______________________________________
White shows an aircraft engine mount providing isolation from vertical vibrations. Parkinson et al. show an arrangement where the engine is anchored not only in the vertical, lateral, and fore and aft senses, but also against angular movement in its pitch, roll, and yaw senses, in the event of partial or total failure of any on element of the attachment arrangement. Schmidt et al. show an engine mounting system for helicopters which has elastomeric mounts for vibration isolation; the system includes a torque tube which is mounted to bodies of a suitable elastomer.
Accordingly, a need exists for a torque box for use with thrust reverser assemblies which significantly reduces the number of individual details employed in its fabrication, and which also provides for reduced weight. Furthermore, a need exists for such a torque box which provides for more effective transmission of both torque and tension loads which are created by the operation of the reverse thruster assembly.